Electromagnetic pump or conveyor trough

ABSTRACT

An electromagnetic pump or conveyor trough for generating a traveling magnetic field by means of current carried by conductors mounted in slots in the bottom of the trough to move an electrically conductive liquid wherein a first hollow tubular conductor having its bore eccentrically offset toward the bottom of the slot and a second hollow tubular conductor with a height which does not substantially exceed the electromagnetic penetration depth are mounted atop each other in each slot with the second conductor nearest the open end of the slot.

United States Patent Von Starck 1 Feb. 29, 1972 [54] ELECTROMAGNETICPUMP OR [56] References Cited CONVEYOR TROUGH UNITED STATES PATENTS [72]Inventor: Axel V n S r k, R mh i -L 2,865,291 12/1958 Cuatt ..417/50tringhausen, Germany 3,045,599 7/1962 Carlson, Jr. et aim. ....4l7/503,052,097 9/1962 Tyrner ....4l7/50 [731 Assgnee- AEGEMhem Remsched'3,534,886 10/1970 Von Starch ..222/70 Hasten, Germany 1 22 Filed: Feb.12 1970 Primary ExaminerWilliam L. Freeh Attorney-Cushman, Darby &Cushman [21] Appl. No.: 10,793

. [57] ABSTRACT [30] Foreign Application Priority Data Anelectromagnetic pump or conveyor trough for generating a v travelingmagnetic field by means of current carried by con- Feb. I2, 1969 Germany..P 19 06 922.8 ductors mounted in Slots in the bottom of the trough tomove. 1 an electrically conductive liquid wherein a first hollow tubular1 Cl --4l7/50 conductor having its bore eccentrically offset toward thebot- [Sl] Int. Cl. ....C2lb 7/14, F27b 3/18 tom of the slot and a secondhollow tubular conductor with a [58] Field of Search. ..417/50; 222/70;198/41; height hich does ot substantially exceed the electromag- 2 /33netic penetration depth are mounted atop each other in each slot withthe second conductor nearest the open end of the slot.

PATENTEDFEB29 I972 SHEET 1 0F 2 In venlar: 44/52 Va 57420:

A IDA/EYJ M PATENTEDFEB29 I972 3, 645,646

sum 2 0F 2 1 ELECTROMAGNETIC PUMP OR CONVEYOR TROUGII This inventionrelates to electromagnetic pumps or conveyor troughs which employ atravelling magnetic field to drive an electrically conductive liquid,such as a metal melt,

along a trough. The field induces an electric current in theconductingliquid and this current interacts with the travelling magnetic field togenerate electromotive forces in the conducting liquid which cause theliquid to move along the trough.

The travelling magnetic field is conventionally produced by one or moreinductors which, in principle, can be regarded as linear developments ofthe stator of a conventional alternating current motor which has beencut open on one longitudinal side. Further, these inductorsconventionally consist of a flat, elongated, laminated and slotted sheetiron core and a polyphase winding of electrically conducting materialwhich is inserted into the open slots of the laminated core so as to beelectrically insulated from the core.

The purpose of the polyphase winding is to carry a polyphase alternatingcurrent when the inductor is in operation and to generate a magneticfield which is guided by the magnetically permeable core. The severalphase sections of the polyphase winding are in conventional mannerspatially distributed along the core so that a travelling magnetic fieldis produced.

Usually the employment of such inductors for electromagnetic pumps andconveyor troughs requires a very high current density in the conductorsof the polyphase winding. This high current density results in theconversion of electricity into considerable amounts of heat according to.loules Law and this heat normally must be removed by cooling theconductors in some fashion. Because of this heating problem thepolyphase winding is usually built up of hollow tubular electricalconductors through which a coolant, for example air or water, can becirculated.

For electrical and design reasons it is advantageous to insert two suchtubular conductors, insulated from each other and one above the other,into each slot of the laminated core, the bottom conductor in the slotbeing a direct continuation of the upper conductor of another slot.Conventionally the bottom and the upper conductors in each slot weretubes having the same cross-sectional configuration. However if twotubular conductors in a slot, one above the other, carry an alternatingelectric current, at least two electrical phenomena of interest occur.First, because of the alternating magnetic field which is generated bythe electrical current in the tubular conductors themselves, and whichlies across the slot, the current in the conductors is displaced towardsthe open side of the slot. The extent of this displacement may becalculated, and depends upon the frequency of the current and thematerial from which the conductors are made. Further, this displacementis determined by the so-called electromagnetic penetration depth, whichis expressed in units of length and which represents the thickness ofthe layer below the conductor surface in which the entire current may bethought to flow in uniform distribution. For copper at room temperatureconducting current at a frequency of 50 c./s. the penetration depth isabout 1 centimeter. The displacement of the current reduces theavailable conductor cross section for carrying current and thus leads toincreased heat production.

Second, the tubular conductor nearest the open side of the slot isexposed to the alternating magnetic field produced by the conductor inthe bottom of the slot. This field transversely crosses the slot andinduces additional eddy currents in the upper conductor. These eddycurrents cause further resistive heating.

It is the object of the invention to geometrically design the twotubular conductors in each slot of the laminated sheet iron core of anelectromagnetic pump or conveyor trough so that the hereinbeforedescribed unfavorable effects which reduce the electrical efficiency ofthe arrangement are minimized. According to the invention this isachieved by providing the two conductors with different cross sections,the conductor at the bottom of the slot having a bore which iseccentrically displaced towards the bottom of the slot. Furthermore, itis proposed that the height of the tubular conductor near the open sideof the slot should be so limited that it does not substantially exceedthe electromagnetic penetration depth. By the selection of these specialcross sections for the conductors, the electrical efficiency of a troughprovided with such conductors is considerably better than troughs havingconductors of identical cross section. Although current displacementstill occurs, the current density in any part of either of the twoconductors does not become excessive, nor are eddy currents induced inthe upper conductor to the extent as in conventional troughs withconductors of identical cross section.

The invention is further elucidated in the following description andillustrated in the accompanying drawing of which:

FIG. 1 is a longitudinal section of the prior art electromagnetic pumpor conveyor trough with conductors having identical cross sections;

FIG. 2 is a longitudinal section of an arrangement according to thisinvention; and

FIG. 3 is a cutaway view of a furnace body with a travelling fieldconductor according to this invention serving as an agitating coil.

Referring to FIG. 1, the laminated sheet iron core I is held together bytie bolts 2 and is located below a trough R which is preferably made ofrefractory material in which the liquid metal Mis conveyed. Each of theslots 3 in the laminated core 1 conventionally contains two hollowtubular conductors 4 which have identical cross sections. The conductorseach have a substantially square bore 6 and are electrically separatedfrom each other and from core 1 by an interposed insulation 8. Thedisadvantages of this arrangement are pointed out above.

FIG. 2 shows a similar section of a trough equipped with hollow tubularconductors l9 and 20 in each slot 13 of core 11. The core 11 and slots13 are preferably of the same material as the core I and slots 3 in FIG.1, and as in FIG. 1, core 1 is held together by tie bolts 12. However,in contrast to FIG. 1, the bore 16 of conductor 19 is not centrallylocated but rather the circular bore 16 of the conductor 19 at thebottom of slot 13 is eccentrically displaced towards the bottom of slot13. Further, the conductor 19 and slot 13 both have a rounded bottom incontrast to the flat bottom in FIG. 1. Moreover, the height 17 ofconductor 20, measured in the direction of the depth of the slot, islimited so that it does not substantially exceed the electromagneticpenetration depth and is substantially less than the height of conductor19. Conductor 19 also has a bore 21 which is smaller than the bore 4 inFIG. 1 and which has a rectangular cross section. 1 Accordingly, thecross sections of the conductors 19 and 20 are not identical as in theprior art embodiment of FIG. 1 and the abovementioned problems whichresulted from the use of conductors as in FIG. 1, are substantiallyalleviated by these specific cross-sectional configurations. It shouldbe apparent that while both configurations are preferably used, eithercan be employed by itself.

FIG. 3 illustrates a cutaway view of a furnace body with a travelingfield inductor according to this invention serving as an agitating coil.Furnace includes a self-supporting fire resistant setting 111, which, asis customary, is enclosed by a furnace wall 112, and which rests on afurnace frame 113. Below the floor of the setting 111, and mounted inthe frame 113, is the traveling field inductor shown in cross sectionwith its stack of sheets 114 and conductors 109 and 110, which areconnected with the inductor winding in the winding head 115. Conductors109 and 110 are disposed in the sheets in the fashion shown in detail inFIG. 2. In order to avoid destruction of the induction winding throughemergence of the liquid metal in the case of breakthrough of thefire-resistant setting 111, partition 116 made of nonmagnetic materialis disposed between the bottom of the setting I11 and the inductor, thepartitioning sheet on its part being preferably separated from theinductor by a layer made of insulated material.

To move the metal melt 117 located in the furnace body, the inductor isswitched, for example, in such a way that it produces an electromagnetictraveling field progressing perpendicularly out of the plane of thedrawing. In the area of the penetrating depth of this traveling field, acurrent in the same direction is produced in the metal melt 117, saidcurrent hav ing been indicated by l 18, and which induces in theremaining areas of the melt a backflow in approximately the oppositedirection. Because of the effect produced by the wall of the furnacesetting, additional flow components are produced thereby in such a waythat altogether a very effective agitation of the metal melt 117 will beachieved.

Many modifications and changes in the embodiment of the inventionillustrated in FIG. 2 can be made without departing from the scope ofthe invention. Accordingly, that scope is intended to be limited only bythe scope of the appended claims.

Thus, with this novel arrangement, the magnetic field required forconveying the metal melt can be generated with the expenditure of aminimum amount of electrical power.

What is claimed is:

1. An electromagnetic conveyor for generating a travelling magneticfield so as to move an electrically conductive liquid in a cavity of abody which holds said liquid comprising:

a core having a plurality of slots, each having an open end,

a plurality of first tubular conductors each mounted in a slot and eachhaving a bore and a plurality of second tubular conductors, each mountedin a slot below said first conductor so that each said first conductoris closer to the open end of the slot than the second conductor in thesame slot and each said second conductor having a bore eccentricallyoffset from the center of said first conductor so as to be closer to thebottom of said slot than to the first conductor in said slot.

2. A conveyor as in claim 1 wherein the height of said first tubularconductors does not substantially exceed the electromagnetic penetrationdepth of said first conductors.

3. A conveyor as in claim 1 wherein the bores of said second conductorshave a circular cross section.

4. A conveyor as in claim 1 including means for insulating the first andsecond conductors in each slot from each other and from said core.

5. A conveyor as in claim 1 including a trough of refractory materialabove said core.

6. A conveyor as in claim 1 wherein said first tubular conductors eachhave a bore of substantially rectangular cross section.

7. A conveyor as in claim 1, including said body and wherein said bodyis a trough made of refractory material.

8. A conveyor as in claim 1, including said body and wherein said bodyis a furnace.

9. A conveyor as in claim 1 wherein said core is laminated sheet iron.

10. A conveyor as in claim 9 including a tie bolt holding said laminatedcore.

11. An electromagnetic conveyor for generating a travelling magneticfield so as to move an electrically conductive liquid in a cavity of abody-which holds said liquid comprising:

a laminated sheet iron core having a plurality of slots, each having anopen end, plurality of first tubular conductors each mounted in a slot,each having a bore, and each having a height in said slot which does notsubstantially exceed the electromagnetic penetration depth of said firstconductors,

a plurality of tubular conductors, each mounted in a slot below saidfirst conductor so that said first conductor is closer to the open endof the slot than the second conductor in the same slot and each saidsecond conductor having a circular bore eccentrically offset from thecenter of said first conductor so as to be closer to the bottom of saidslot than to the first conductor in said slot means for insulating saidfirst and second conductors in each slot from each other and from saidcore.

1. An electromagnetic conveyor for generating a travelling magneticfield so as to move an electrically conductive liquid in a cavity of abody which holds said liquid comprising: a core having a plurality ofslots, each having an open end, a plurality of first tubular conductorseach mounted in a slot and each having a bore and a plurality of secondtubular conductors, each mounted in a slot below said first conductor sothat each said first conductor is closer to the open end of the slotthan the second conductor in the same slot and each said secondconductor having a bore eccentrically offset from the center of saidfirst conductor so as to be closer to the bottom of said slot than tothe first conductor in said slot.
 2. A conveyor as in claim 1 whereinthe height of said first tubular conductors does not substantiallyexceed the electromagnetic penetration depth of said first conductors.3. A conveyor as in claim 1 wherein the bores of said second conductorshave a circular cross section.
 4. A conveyor as in claim 1 includingmeans for insulating the first and second conductors in each slot fromeach other and from said core.
 5. A conveyor as in claim 1 including atrough of refractory material above said core.
 6. A conveyor as in claim1 whereIn said first tubular conductors each have a bore ofsubstantially rectangular cross section.
 7. A conveyor as in claim 1,including said body and wherein said body is a trough made of refractorymaterial.
 8. A conveyor as in claim 1, including said body and whereinsaid body is a furnace.
 9. A conveyor as in claim 1 wherein said core islaminated sheet iron.
 10. A conveyor as in claim 9 including a tie boltholding said laminated core.
 11. An electromagnetic conveyor forgenerating a travelling magnetic field so as to move an electricallyconductive liquid in a cavity of a body which holds said liquidcomprising: a laminated sheet iron core having a plurality of slots,each having an open end, a plurality of first tubular conductors eachmounted in a slot, each having a bore, and each having a height in saidslot which does not substantially exceed the electromagnetic penetrationdepth of said first conductors, a plurality of tubular conductors, eachmounted in a slot below said first conductor so that said firstconductor is closer to the open end of the slot than the secondconductor in the same slot and each said second conductor having acircular bore eccentrically offset from the center of said firstconductor so as to be closer to the bottom of said slot than to thefirst conductor in said slot means for insulating said first and secondconductors in each slot from each other and from said core.